Ultrafine Particles

Introduction

Characteristics of Ultrafine Particles

Transport and Fate in the Environment

Measuring Exposure

Exposure Pathways

Prevention or Control of Exposures

Human Health Effects of Ultrafine Particles


Effects

Absorption and Distribution

Biomarkers

Risk Assessment

Works Cited


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Measuring Exposure

Measuring exposure requires a variety of measurement methods involving both the ambient air in the environment as well as the measurement of exposure to the indivual. This section describes the methods used to measure UFP’s in the environment and to evaluate human exposure.

Environmental Exposure
For indirect measurements monitoring networks are important sources for pollutant concentration information. These are established to provide warnings for pollution episodes, estimate source contributions, process studies, and to understand trends in pollution concentrations. Urban monitoring networks consist of street locations where compounds emitted by traffic and local industry are measured. It is anticipated that ultrafine particulate matter will become a standard parameter in particulate monitoring.

Urban background monitoring stations are now used in conjunction with hotspot sites to aid in model evaluation and to provide information on rural background concentrations of air pollution.

The measurement of ultrafine particles (UP’s) is highly complex and generally involves sophisticated equipment. There are presently no commercial “spectrometers” for long-term measurement of aerosol (Khlystov et al., 2001). As a result, home-built of modified research instrumentation is used to collect ambient UP data air quality data (Khylystov et al., 2001). Typically, this includes a combination of spectrometers and condensation particle counters using a variety of measurement methods.

In the United Kingdom, Tapered Element Oscillating Microbalance techniques are utilized for ultrafine particulate detection6. The advantage of the TEOM is its ability to provide data in real time. The TEOM collects particles on a filter attached to an oscillating microbalance. The frequency of vibration of the balance is dependent on the mass of the filter. This technique has the drawback of heating the sample to 50 C to remove water. One of the most widely used, the TEOM, underestimates mass of ultrafine particulate due to the loss of volatile matter at the detectors operating temperature. Sulfate ion concentration is detected using ion chromatography. Total inorganic nitrate concentrations were measured using open cellulose filters impregnated with sodium hydroxide.

References:

McLachlan, J 2001 Environmental signaling: what embryos and evolution teach us about endocrine disrupting chemicals. Endocrine Reviews 22.3 (2001): 319-341

Hutchinson, Thomas H et al. Ecological Risk Assessment of Endocrine Disruptors. Environmental Health Perspectives 108.11 (2000): 1007-1014

Safe, Stephen H. Endocrine Disruptors and Human Health-Is There a Problem? An Update. Environmental Health Perspectives 108.6 (2000): 487-493

Keith Lawrence H, Jones-Lepp Tammy L, Needham Larry L. Analysis of Environmental Endocrine Disruptors. Washington DC: Oxford University Press, 2000.


Human Exposure
Exposure to ultrafine particles is felt to be a major health concern for humans. The classic example of adverse health effects on humans from particulate pollution is the London smog episode of 1952 (Wilkins et al., 1954). Modern conditions in the urban environment, primarily because of poor dispersion and increased density of pollution sources, have led to very high levels of particulate pollution. Assessment of exposure levels and is imperative to understanding health effects. Proper measurement of exposure, however, can often be difficult. Measuring exposure can be done by use of categorical classification, application of biomarkers, analysis of air pollution data from routine monitoring networks, personal portable exposure monitors, or application of exposure models (Herber et al., 2001).

Human exposure can be determined by direct of indirect methods. Direct methods are made using personal portable exposure monitors, or by using biological markers. Indirect methods are made by measuring concentrations at specific times in known locations. In applying the indirect measurement method, the concept of microenvironment is used. This is a three-dimensional space with uniform statistical properties. The distinction between exposure and dose is often helpful. Dose is the mass of pollution that crosses the body’s boundary and reaches the target tissue (Sexton and Ryan, 1988).

To understand exposure measurement it is useful to define some of the key terms used (IUPAC glossary):

  • Concentration—mass per volume of air.
  • Mass mixing ratio—mass of substance per mass of air.
  • Exposure—contact with a concentration of pollutant.

Magnitude, duration, and frequency are important parameters to be measured for exposure determination.

Sometimes measuring an individual’s exposure to a pollutant can be relatively straightforward, but often in public health, measuring aggregated exposure in a population group is of interest. The most common approach is to use the indirect method of combining pollutant concentrations observed at various microenvironments. To do this requires several assumptions7:

  • concentration is assumed constant;
  • concentration and presence of person are independent events;
  • the number of microenvironments is traceably small;
  • disregard for high-frequency short-term peaks; and,
  • indoor concentrations are often estimated from outdoor concentrations.

Measurements of ultrafine particulate concentrations can be done using small, portable personal exposure monitors. These devices can be integrated (results measured in laboratory) or continuous (self-analysis). They can be active or passive. Passive samplers are available for carbon monoxide, nitrogen oxides, ozone, and benzene, and larger sized particulate matter. A disadvantage to personal monitoring for large-scale pollution monitoring is that people generally spend an inordinate amount of time indoors, and device measurements do not generally reflect outdoor air concentrations.

References:

McLachlan, J 2001 Environmental signaling: what embryos and evolution teach us about endocrine disrupting chemicals. Endocrine Reviews 22.3 (2001): 319-341

Hutchinson, Thomas H et al. Ecological Risk Assessment of Endocrine Disruptors. Environmental Health Perspectives 108.11 (2000): 1007-1014

Safe, Stephen H. Endocrine Disruptors and Human Health-Is There a Problem? An Update. Environmental Health Perspectives 108.6 (2000): 487-493

Keith Lawrence H, Jones-Lepp Tammy L, Needham Larry L. Analysis of Environmental Endocrine Disruptors. Washington DC: Oxford University Press, 2000.